Γ-ray Fields Research Articles

Development of a silicon carbide radiation detection system and experimentation of the system performance

Silicon carbide (SiC) detectors have excellent radiation detection capabilities for various radiation particles, including high energy resolution, fast response times, and good radiation resistance. A SiC radiation detection system was developed to measure the neutron fluence rate and the γ-ray dose rate in high intensity radiation fields. The system was composed of two SiC detectors, a temperature monitor, two preamplifiers for each SiC detector, a data acquisition unit with two signal channels, three pairs of communication devices, and an application software to analyze and visualize the measurement data. The two SiC detectors were fabricated based on two kinds of 4H-SiC diodes and used to respectively respond to neutrons and γ-rays. Repeated experiments showed that the two SiC detectors of the system can respond to α-particles, neutrons, and γ-rays. To verify the performance of the SiC detection system, including the response linearity of the neutron fluence rate, the measurement range of the γ-ray dose rate, and the radiation resistance of the SiC radiation detectors, the system was tested in multiple neutron and γ-ray fields. The tests results show the system can measure the neutron fluence rate from 5.64 × 10 2 cm−2 s−1 to 1.03 × 10 5 cm−2 s−1 with excellent linearity response, and the γ-ray dose rate from 0.005 Gy/h to 20 Gy/h. Furthermore, the SiC detectors demonstrated good radiation resistance. The neutron and γ-ray radiation field can still be measured stably by the system after exposure to neutron fluence of 1.07 × 10 14 cm−2 and γ-ray dose of 3.52 × 10 4 Gy. This work is the preliminary research to continue the exploration how to measure the n/γ hybrid fields accurately using SiC detectors considering the different energy of neutrons.

Neutron/[formula omitted]-ray discrimination based on the property and thickness controls of scintillators using Li glass and LiCAF (Ce) in a [formula omitted]-ray field

Recently, various neutron detectors, such as scintillation detectors, are being developed as alternatives to 3He proportional counters. Here we focus on the thickness and property controls of inorganic scintillators used for thermal neutron detection in intense γ-ray fields without considering pulse shape discrimination (PSD) techniques. GS20TM (a lithium glass) and LiCaAlF6 crystals activated with Ce (LiCAF:Ce) scintillators with thicknesses of 0.5 and 1.0 mm, respectively, have been employed because they have faster decay times than other inorganic scintillators. Pulse signals generated by photomultiplier tubes, to which the scintillators were coupled, were inserted into a digital pulse processing unit with a sampling rate of 1 GHz, and the areas of waveforms were integrated for 360 ns. Neutron/γ-ray detections and discriminations were performed via pulse integrations without using PSD techniques. For GS20TM, the relative energy resolution values of the thermal neutron peaks were 11% and 12% in 0.5 mm and 1.0 mm thicknesses, respectively, and those for LiCAF:Ce were 18% and 36% in 0.5 mm and 1.0 mm thicknesses, respectively. In a 60Co γ-ray field, the neutron detection for GS20TM in a 0.5 mm thickness was possible at dose rates of up to 0.919 Gy/h; however, for LiCAF:Ce, neutron detection was possible at 0.473 Gy/h, and it failed at 0.709 Gy/h. The neutron/γ-ray discrimination of GS20TM was better than that of LiCAF:Ce due to its better energy resolution and higher detection efficiency (6Li content).

Identifying γ-ray emitting blazars in the PASIPHAE era: polarimetry as a unique probe

AbstractThe Fermi γ-ray telescope has detected 6658 sources, with 1845 of them remaining unidentified. We show that polarimetry of γ-ray fields is a powerful asset in the hunt of active galactic nuclei (AGN) as potential optical counterparts for γ-ray sources. We have studied an unidentified Fermi field (3FGL J0221.2+2518) and found a previously-unknown highly-polarized extragalactic object as a potential optical counterpart within the 1-sigma error ellipse of the corresponding γ-ray source. Based on a collection of data, we find that it most probably is a composite object: a star-forming galaxy accompanied by AGN. PASIPHAE is a large polarimetric experiment which will measure the polarisation of sources away from the galactic plane. This will provide an excellent opportunity to study hundreds of unidentified γ-ray sources and unveil potential optical counterparts, using polarimetry.

Celebrating 60 Years of Accomplishments of the Armed Forces Radiobiology Research Institute1.

Chartered by the U.S. Congress in 1961, the Armed Forces Radiobiology Research Institute (AFRRI) is a Joint Department of Defense (DoD) entity with the mission of carrying out the Medical Radiological Defense Research Program in support of our military forces around the globe. In the last 60 years, the investigators at AFRRI have conducted exploratory and developmental research with broad application to the field of radiation sciences. As the only DoD facility dedicated to radiation research, AFRRI's Medical Radiobiology Advisory Team provides deployable medical and radiobiological subject matter expertise, advising commanders in the response to a U.S. nuclear weapon incident and other nuclear or radiological material incidents. AFRRI received the DoD Joint Meritorious Unit Award on February 17, 2004, for its exceptionally meritorious achievements from September 11, 2001 to June 20, 2003, in response to acts of terrorism and nuclear/radiological threats at home and abroad. In August 2009, the American Nuclear Society designated the institute a nuclear historic landmark as the U.S.'s primary source of medical nuclear and radiological research, preparedness and training. Since then, research has continued, and core areas of study include prevention, assessment and treatment of radiological injuries that may occur from exposure to a wide range of doses (low to high). AFRRI collaborates with other government entities, academic institutions, civilian laboratories and other countries to research the biological effects of ionizing radiation. Notable early research contributions were the establishment of dose limits for major acute radiation syndromes in primates, applicable to human exposures, followed by the subsequent evolution of radiobiology concepts, particularly the importance of immune collapse and combined injury. In this century, the program has been essential in the development and validation of prophylactic and therapeutic drugs, such as Amifostine, Neupogen®, Neulasta®, Nplate® and Leukine®, all of which are used to prevent and treat radiation injuries. Moreover, AFRRI has helped develop rapid, high-precision, biodosimetry tools ranging from novel assays to software decision support. New drug candidates and biological dose assessment technologies are currently being developed. Such efforts are supported by unique and unmatched radiation sources and generators that allow for comprehensive analyses across the various types and qualities of radiation. These include but are not limited to both 60Co facilities, a TRIGA® reactor providing variable mixed neutron and γ-ray fields, a clinical linear accelerator, and a small animal radiation research platform with low-energy photons. There are five major research areas at AFRRI that encompass the prevention, assessment and treatment of injuries resulting from the effects of ionizing radiation: 1. biodosimetry; 2. low-level and low-dose-rate radiation; 3. internal contamination and metal toxicity; 4. radiation combined injury; and 5. radiation medical countermeasures. These research areas are bolstered by an educational component to broadcast and increase awareness of the medical effects of ionizing radiation, in the mass-casualty scenario after a nuclear detonation or radiological accidents. This work provides a description of the military medical operations as well as the radiation facilities and capabilities present at AFRRI, followed by a review and discussion of each of the research areas.

Gamma-ray spectroscopy with a CeBr3 scintillator under intense [formula omitted]-ray fields for nuclear decommissioning

Recently, an increasing number of nuclear facilities have been decommissioned worldwide following the 2011 accident of the Tokyo Electric Power Company Holdings’ Fukushima Daiichi Nuclear Power Station. However, large amounts of radioactive wastes and spent nuclear fuels remain on these facilities, leading to intense radiation fields. During the decommissioning processes, radioactive wastes and spent nuclear fuels have to be retrieved under proper management, and γ-ray spectroscopy supports this process. In this study, a small cubic CeBr3 spectrometer with dimensions of 5 mm × 5 mm × 5 mm was manufactured to perform γ-ray spectroscopy under intense γ-ray fields. Furthermore, thanks to both: (1) a digital process unit with sampling rate of 1 Giga samples per second; and, (2), a photomultiplier assembly featuring individual voltages supplied to the last three stages; the device successfully performed γ-ray spectroscopy up to at dose rates of over 1 Sv/h. The energy resolution (full width at half maximum) at 662 keV ranged from 4.4% at 22 mSv/h to 5.2% at 1407 mSv/h for a 137Cs radiation field. Correspondingly, at 1333 keV, it ranged from 3.1% at 26 mSv/h to 4.2% at 2221 mSv/h for a 60Co radiation field. The energy resolution met the requirements to solve the prominent γ-ray spectral lines of 134Cs, 137Cs, 60Co, and 154Eu. These results suggest that the detector has the potential to realize the γ-ray assessment of 134Cs, 137Cs, 60Co, and 154Eu at dose rates of over 1 Sv/h.

Studying the Radiation Hardness of the Control System Components for the Forward Calorimeter in the PANDA Experiment

Analog-to-digital converter chips used in the Cockcroft−Walton generators of the forward calorimeter in the PANDA experiment have been tested for radiation hardness in γ-ray and neutrons fields. The radiation hardness of temperature sensors under exposure to a neutron flux has also been investigated.

Development of a neutron imager based on superconducting detectors

We succeeded in demonstrating a neutron detector based on a Nb superconducting meander line with a 10B conversion layer for a neutron imager based on superconductor devices. We use a current-biased kinetic inductance detector (CB-KID), which is composed of a meander line, for detection of a neutron with high spatial resolution and fast response time. The thickness of Nb meander lines is 40 nm and the line width is narrower than 3 mu m. The area of 8 mm × 8 mm is covered by CB-KIDs, which are assembled at the center of the Si chip of the size 22 mm × 22 mm. The Nb CB-KIDs with a 10B conversion layer output the voltage by irradiating pulsed neutrons. We have investigated γ/n discrimination of a Nb-based CB-KID with 10B conversion layer using a Cd plate, which indicates that a CB-KID can operate as a neutron detector under the strong γ-ray fields.

Jumpwise deformation of polymethyl methacrylate in the microplasticity region

The deformation rate with a step of 325 nm has been measured under uniaxial compression at the initial stage of creep and shape recovery of a polymethyl methacrylate (PMMA) sample after unloading. The effect of low γ-ray doses and magnetic fields on the deformation has been studied. It has been shown that a weak pre-exposure of the PMMA sample structure to radiation and magnetic fields can cause a slight hardening in the microplasticity region. The deformation jump sizes have been determined on micro- and nanoscales. The effect of irradiation and magnetic fields manifests itself as redistributed contributions of various jumps to the deformation.

Deficiency in Monte Carlo simulations of coupled neutron ‐γ-ray fields

The deficiency in Monte Carlo simulations of coupled neutron-γ-ray field was investigated by benchmarking two simulation codes with experimental data. Simulations showed better correspondence with the experimental data for γ-ray transport only. In simulations, the neutron interactions with matter lead to the production of secondary neutrons and γ-rays based on available cross section data libraries. In both the simulation and experiment, the resulting γ-ray spectra could be qualitatively explained based on probable reactions. However, a quantitative analysis was unsuccessful due to deviations in spectral shape and intensities, and thus restricting the use of this technique. The deviations can likely be attributed to the mode of operation of the codes, partly the way the neutrons generate γ-rays and partly the way the γ-rays are being binned.

Measurements of neutron distribution in neutrons–γ-rays mixed field using imaging plate for neutron capture therapy

The imaging plate (IP) technique is tried to be used as a handy method to measure the spatial neutron distribution via the 157Gd(n,γ) 158Gd reaction for neutron capture therapy (NCT). For this purpose, IP is set in a water phantom and irradiated in a mixed field of neutrons and γ-rays. The Hiroshima University Radiobiological Research Accelerator is utilized for this experiment. The neutrons are moderated with 20-cm-thick D 2O to obtain suitable neutron field for NCT. The signal for IP doped with Gd as a neutron-response enhancer is subtracted with its contribution by γ-rays, which was estimated using IP without Gd. The γ-ray response of Gd-doped IP to non-Gd IP is set at 1.34, the value measured for 60Co γ-rays, in estimating the γ-ray contribution to Gd-doped IP signal. Then measured distribution of the 157Gd(n,γ) 158Gd reaction rate agrees within 10% with the calculated value based on the method that has already been validated for its reproducibility of Au activation. However, the evaluated distribution of the 157Gd(n,γ) 158Gd reaction rate is so sensitive to γ-ray energy, e.g. the discrepancy of the 157Gd(n,γ) 158Gd reaction rate between measurement and calculation becomes 30% for the photon energy change from 33 keV to 1.253 MeV.

Improvement of a Gas Scintillation Proportional Counter

A prototype GSPC without the gas purification system was developed in China Institute for Radiation Protection(CIRP). Xenon filled GSPC has many advantages, including high energy resolution, large detection area, ability for implementing position sensitive detection, etc. It may find a wide application in low energy X-ray and γ-ray fields, e.g., astronomy X-ray detection, medical imaging. Further applications in neutron and charged heavy particle detection are also possible. Several tests for 241Am and 55Fe have been carried out to check out its preliminary performance. Currently the energy resolution is still far from expectation, nevertheless, the concept is proved to be promising and the experimental results suggest the way for further improvements. The possible ways for improvement of the detector performance are discussed in conclusion. This work was funded by National Natural Science Foundation of China.Authorization number:10375054(National Natural Science Foundation of China).

Characteristics of neutron and gamma radiation in the core of the ΦC-1-4.37.P critical assembly

The characteristics of neutron and γ-ray fields (spectrum, flux density, average energy, cross sections of 23 nuclear reactions, and γ-ray dose rate) and the γ-ray field in the core of the ΦC-1-4.37.P critical assembly of the ΦC-1M critical bench are determined. The results of comparing the characteristics of the neutron fields of the ΦC-1-4.37.P critical assembly and analogous reactors are presented.

Physical parameters and correction factors for ionization chambers for absolute measurement of air kerma in γ-ray fields

Values of physical parameters and correction factors essential for the absolute measurement of air kerma in 137Cs and 60Co γ-ray fields were obtained using an EGS5 program for spherical, cylindrical and pancake ionization chambers. The mean mass collision stopping power ratio for graphite and air, was found to vary depending on the cutoff energy of electrons employed in calculation. The ratio between the energies deposited in cavity air due to Compton electrons emitted from the air and those from the graphite wall increases as the chamber size is increased. It also increases as the γ-ray energy is reduced and is equal to 0.09 for 137Cs γ-rays in a spherical ionization chamber of cavity diameter 12 cm. Correction factors for γ-ray attenuation in chamber walls and those for the contribution of scattered γ-rays to chamber responses were obtained separately. The wall correction factor, which is equal to the product of these two factors, is close to unity for pancake chambers.

Testing a fiber-optic ionizing-radiation detector

A fiber-optic ionizing-radiation detector is composed of a scintillation sensor, an optical fiber, and a photodetector. Due to the miniature size and the high radiation resistance, the detector is capable of measuring the characteristics of powerful neutron and γ-ray fields with a high spatial resolution. A prototype of the detector has been tested using a 60Co γ-ray source with a dose rate as great as 200 R/S. The dynamic range of dose measurements is no less than 105. The detector signal is linearly dependent on the radiation dose rate. The ratio of the useful signal to the background due to radioluminescence of the optical fiber is presented for different types of scintillators.

The use of ultrasonic properties of cr-39 track detectors in neutron dosimetry

The longitudinal and shear wave ultrasonic velocities have been measured before and after exposing 5-mm thick CR-39 solid state nuclear track detectors to both a mixed field of γ-rays and fast neutrons from an Am-Be source in the ranges from 0 to 104 mSv. The change in the intermolecular structure as caused by the fast neutron exposure was studied by the ultrasonic pulse echo method at a frequency of 2 MHz and at room temperature. The elastic coefficients, Poisson's ratio, microhardness, ultrasonic absorption coefficient and internal friction have been determined. The study shows that the γ-ray irradiation had no effect on the ultrasonic properties of CR-39 at least at the used doses. However, all the ultrasonic properties are influenced by the fast neutrons at doses up to 104 mSv. Our experimental results confirmed that the ultrasonic technique is useful for fast neutron detection, by exploiting the differences in mechanical properties of CR-39.

An application of artificial neural intelligence for personal dose assessment using a multi-area OSL dosimetry system

Significant advances have been made in recent years to improve measurement technology and performance of phosphor materials in the fields of optically stimulated luminescence (OSL) dosimetry. Pulsed and continuous wave OSL studies recently carried out on α-Al 2O 3 : C have shown that the material seems to be the most promising for routine application of OSL for dosimetric purposes. The main objective of the study is to propose a new personal dosimetry system using α-Al 2O 3 : C by taking advantage of its optical properties and energy dependencies. In the process of the study, a new dose assessment algorithm was developed using artificial neural networks in hopes of achieving a higher degree of accuracy and precision in personal OSL dosimetry system. The original hypothesis of this work is that the spectral information of an X- and γ-ray fields may be obtained by the analysis of the response of a multi-element system. In this study, a feedforward neural network using the error back-propagation method with Bayesian optimization was applied for the response unfolding procedure. The validation of the proposed algorithm was investigated by unfolding the 10 measured responses of α-Al 2O 3 : C for arbitrarily mixed photon fields which range from 20 to 662 keV.

Characteristics of γ-ray fields above137Cs-contaminated soil surface

Characteristics of γ-ray fields above137Cs-contaminated soil surface

Dependence of TLD thermoluminescence yield on absorbed dose in a thermal neutron field

The emission from 6LiF and 7LiF thermoluminescence dosimeters (TLDs) exposed to the mixed field of thermal neutrons and γ-rays of the thermal facility of a TRIGA MARK II nuclear reactor has been investigated for various thermal neutron fluences of the order of magnitude of those utilised in radiotherapy, with the purpose of investigating the reliability of TLD readouts in such radiation fields and of giving some information for better obtainment of the absorbed dose values. The emission after exposure in this mixed field is compared with the emission after γ-rays only. The glow curves have been deconvoluted into gaussian peaks, and the differences in the characteristics of the peaks observed for the two radiation fields, having different linear energy transfers, and for different doses are shown. Irreversible radiation damage in dosimeters having high sensitivity to thermal neutrons is also reported, showing a memory effect of the previous thermal neutron irradiation history which is not restored by anneal treatment.

Study of optical and electrophysical characteristics of cerium-containing glasses

The jumping conductivity ( σ c) on localized states close to the Fermi level at T < 200°C and the ionic conductivity ( σ i) at T > 250°C have been established in the alumina-silica alkalineless cerium-containing glasses. The charge transfer is realised by electron jumping on the scheme Ce 3+ ↔ Ce 4+ ( σ c and by the alkaline-earth cations ( σ i). In the 60Co γ-ray fields σ c increases according to the law σ c = AP Δ where P is the dose rate and Δ < 0.5 at P < 800 R/s and Δ > 1 at P > 800 R/s, while σ i decreases because of the decrease in the number of charge carriers owing to the electron-ion recombination, as P grows. Increase in the concentration ( C) of CeO 2 in the composition of the glass was found to enhance the degree of cerium oxidation and to cause the simultaneous presence of Ce 3+ and Ce 4+ in the structure with the predominant entry of Ce 4+ at a concentration of Ceo 2 > 4.5 mol%. The increase of the concentration of CeO 2 to 9 mol% and the substitution chain of Mg 2+ → Sr 2+ → Ba 2+ in the glass composition lead to a drop in the luminescence intensities, correlated with the decrease of σ due to the transition Ce 3+ → Ce 4+ and suppressive action of Sr 2+ and Ba 2+. The kinetics of Ce 3+ ↔ Ce 4+ transformation under the irradiation have been considered.

On the response functions of NaI(Tl) detectors to terrestrial gamma-radiation

A computer program is described for the calculation of detector efficiency and energy deposition spectra for scintillation crystals irradiated by isotropic or semi-isotropic γ-ray fields. The Monte-Carlo models used in the calculations are valid for γ-ray energies ⩽ 3.0 MeV (the case of terrestrial γ-radiation). Results of computations for four different NaI(Tl) crystals are presented in the form of tables. A comparison is given between a calculated spectrum of uranium measured in 2 π geometry by a 1.75 × 2″ probe and experimental results.